The present invention relates to a magnetic damper using a magnetic force as a braking force, and an actuator having the damper.
When an output shaft of an actuator is to be stopped at a stroke end, it is general to bring an operating element which is mounted on the shaft and moves together with the shaft into abutment against the damper. In this case, in order to moderate an impact at the time of abutment, various dampers are used.
As such a damper, there is a widely known damper which uses an elastic force of a spring or rubber as a braking force. In the case of this damper, the spring or rubber is compressed when the operating element collides and the elastic force is increased. Thus, the operating element largely bounces by the repulsion, and vibration is repeated until the operating element stops. Therefore, it takes time until the shaft stops at the stroke end, and there is a possibility that precise driving and control operations of the actuator are hindered. Further, since the spring or rubber is elastically deformed whenever the operating element collides, there is a problem that the spring or rubber is damaged while the operating element repeatedly collides and the elastic force is deteriorated, and the endurance is poor.
It is a technical object of the present invention to enhance service conditions and endurance of a damper which damps and stops an operating element of an actuator by reducing a bounce caused when the operating element collides, by shortening time required until the operating element stops, and by reducing damage caused by collision of the operating element.
To achieve the above object, the present invention provides a magnetic damper comprising a movable braking plate for receiving an operating element of an actuator, and a stator for attracting the braking plate by a magnetic force, wherein a magnetic attraction force acting between the stator and the braking plate is used as a braking force for stopping the operating element.
In the magnetic damper having the above-described structure, if the moving operating element collides against the braking plate at the stroke end, the braking plate is displaced in a direction apart from the stator, but since the magnetic attraction force is acting between the braking plate and the stator, the magnetic attraction force acts as a braking force and a kinetic energy of the operating element is absorbed, and the operating element is damped and stopped at the stroke end. At that time, by setting a mass of the braking plate to a large value to some extent, preferably to a value closer to that of the operating element as close as possible, a collision energy when the operating element collides can reliably and efficiently be absorbed by cooperation of the displacement of the braking plate and the magnetic attraction force.
The braking plate which once separated from the stator is pulled back by the magnetic attraction force between the stator and the braking plate, and the braking plate stops at that position together with the operating element.
In the magnetic damper, since the magnetic attraction force between the braking plate and the stator is used as the braking force, a bounce of he operating element is smaller than that of the conventional damper using elastic force of a spring or rubber, and the operating element can be stopped earlier within a short time. Even if the operating element repeatedly collides against the braking plate, neither the magnetic force nor the braking force is deteriorated and endurance is excellent.
In the present invention, the operating element and braking plate maybe able to adsorb each other by a magnetic force. With this, a bounce between the operating element and the braking plate can be suppressed and the operating element can stop in a shorter time.
In this invention, a buffering member may be disposed on an abutment surface of the braking plate with respect to the operating element. With this, it is possible to moderate an impact caused when the operating element collides against the braking plate, and to prevent an impact noise from being generated.
The present invention also provides an actuator having the above-described magnetic damper, in which an operating element that moves together with a member which takes out an output is damped and stopped at the stroke end by the magnetic damper.
In the invention, the actuator may comprise cylindrical yokes having a pair of opposed polar teeth, an exciting coil wound around the yokes, an operating element having a cylindrical permanent magnet which is axially movably disposed in hollow portions of the yokes and which is provided with north pole and south pole polarized in its radial direction, and an output shaft connected to the operating element.
According to a concrete example of the invention, the braking plate is formed into an annular shape and disposed on side surfaces of the yokes such that the braking plate adsorbs the side surfaces, and the shaft passes through the braking plate.